FR2526223A1 - IMPROVED AMORPHOUS SILICON-CONTAINING OXYGEN ALLOYS WITH LARGE BAND AND P-TYPE INTERVAL AND DEVICES FOR USING SAME - Google Patents

Abstract

PHOTOSENSITIVE DEVICE OF THE TYPE INCLUDING SUPERIMPOSED LAYERS OF VARIOUS MATERIALS DEPOSITED ON AN AMORPHIC SEMICONDUCTIVE ALLOY SUBSTRATE FORMING AN ACTIVE AND INTRINSIC PHOTOSENSITIVE LAYER ON WHICH IMPACT THE RADIATIONS TO PRODUCE CHARGE CARRIERS OF AMORPHOUS, AND A LAYER WITH SILICIUM WIDE BAND AND P-TYPE INTERVAL 168 ADJACENT TO THE SAID INTRINSIC LAYER 166, INCLUDING AT LEAST ONE STATE DENSITY-REDUCING ELEMENT, A P-TYPE DOPANT, AND ONE ELEMENT THAT INCREASES THE BAND INTERVAL, A DEVICE IN WHICH THE ELEMENT THAT INCREASES THE BAND INTERVAL IS CONSTITUTED BY OXYGEN.

Description

The invention relates to photovoltaic devices and a method for

  the devices being formed by amorphous semiconductor alloy layers At least one layer of amorphous silicon alloy devices is a layer of amorphous silicon alloy with a wide band gap, or forbidden band, of the type p whose electrical conductivity is improved

  advantage of this approach to the problem is to make it possible

  Increased absorption in the active layers while achieving a better current collection efficiency which facilitates the formation of larger short-circuit currents. Another advantage is that the improved photosensitive characteristics of the fluorine-amorphous silicon alloys can be improved. obtained in a more complete way with the photovoltaic devices

  The present invention is the most important application

  aunt of the invention is the realization of devices

  p-i-n photovolts of silicon alloy

  advanced amorphous acid, in the form of single cells or multiple cells comprising

several individual cells.

  Silicon is the basis of the huge crystalline semiconductor industry and is the material with which high-yield (18 percent) costly crystalline solar cells or cells have been produced for space applications.

  terrestrial applications, solar cells

  tallines typically have much lower yields and are of the order of 12% or less when the 3 U techn 3 lcg'-2 of the S riconductlur F crystal Lins has reached the

  commercial level, it has become the foundation of

  current industry of semiconductor devices.

  This was due to the ability of scientists to grow crystals of germanium and more particularly virtually defect-free silicon, and then transform them

  extrinsic materials containing conductive regions

  This result has been obtained by diffusing into the crystalline material a few parts per million of donor (n) or acceptor (p) doping materials introduced as substitution impurities into substantially pure crystalline materials. in order to increase their electrical conductivity and determine their type of conduction p or n The manufacturing methods used to make pn junction crystals involve extremely complicated processes, time consuming and expensive These are why these crystalline materials that are useful in solar cells and current control devices are produced under very carefully controlled conditions making

  grow individual crystals of silicon or germany

  nîum, and when one needs p-n junctions, by doping the individual crystals with extremely small quantities

and doping criticism.

  These crystal growth processes produce relatively small crystals that solar cells require the assembly of many individual crystals to cover the desired surface of a single solar cell panel. The amount of energy required to make a solar cell according to this The limitations of silicon crystal size limitations, and the need to cut and assemble this crystalline material, have been an economic barrier that can not be overcome to achieve large-scale use of crystalline semiconductor solar cells. In addition, the crystalline silicon has an indirect optical flange causing poor light absorption in the material. Due to this poor absorption of light, the crystalline solar cells must have a thickness at least 50 microns to absorb the ground light Incident Area Even if the mono-crystalline material is replaced by polycrystalline silicon obtained by less expensive methods, the indirect optical flange still exists; therefore, the thickness of the material is not reduced. The polycrystalline material also involves the addition of granular boundaries and other defects.

  problems, which defects are usually harmful

  ble. In short, crystalline silicon devices have fixed parameters which can not be varied as desired, require large amounts of material, can only be produced in the form of

  relatively small area, their manufacture being

  The Amorphous Silicon Based Devices Can Eliminate These Drawbacks of Crystalline Silicon An amorphous silicon alloy includes an optical absorption flange having properties similar to those of a direct gap semiconductor and it is sufficient that the material has a thickness of one micron or less to absorb the same amount of sunlight

  that crystalline silicon having a thickness of 50 microns.

  In addition, amorphous silicon alloys can be obtained faster, more easily and in

  larger area than crystalline silicon.

  As a result, considerable efforts have been made to develop processes for

  easily deposit alloys or semiconducting films

  amorphous cells, each of which can cover relatively

  important if desired and limited only

  the dimensions of the deposit equipment, and which

  The p-n junction devices obtained from the latter would be equivalent to those produced by means of their crystalline counterparts for many years to be easily doped to form n-type and n-type materials.

  years, these works were virtually without results.

  Silicon or amorphous germanium films (Group IV) are normally coordinated four times and found to include micro-voids and unsaturated bonds and other defects producing high density of localized states in their band gap. or band

  The presence of a high density of local

  in the amorphous silicon semiconductor film band gap results in a low degree of photoconductivity and short carrier life, making these films unsuitable for applications where photosensitivity characteristics are used. In addition, these films can not be successfully doped or otherwise modified to shift the Fermi level close to the conduction or valence bands, making them

  unusable to form p-n junctions for

  solar cells or for applications related to

  current control devices.

  As a result of efforts to reduce the problems just mentioned and noted with amorphous silicon (originally thought to be elementary), WE Spear and PG Le Comber du Carnegie Laboratory of Physics, University of Dundee,

  Dundee, Scotland, carried out research on the Subsidiary

  "Doping of Amorphous Silicon"

  amorphous silicon), which was the subject of a report

  published in 'Solid State Communications', Vol 17, pp. 1193-1196, 1975, to reduce the localized states in the band gap of amorphous silicon or germanium and bring them closer to intrinsic crystalline silicon and germanium and to dope by substitution said amorphous materials by means of conventional and appropriate dopants, as for the doping of crystalline materials, to make them of the extrinsic type and of

conduction of type p or n.

  The reduction of localized states was obtained by

  luminescent discharge deposition of amorphous silicon films

  wherein a silane gas (Si H 4) is passed through a reaction tube where the gas is decomposed by high frequency glow discharge and deposited on a substrate having a temperature of about 500 K to 600 K (2270 C to 3270 C) The material thus deposited on the substrate is an intrinsic amorphous material consisting of silicon and

  In order to obtain a doped amorphous material, it has been

  mixed in the silane gas a phosphine gas (PH 3)

  to obtain an n-type conduction, or a dibox gas

  rane (B 2 H 6) to obtain p-type conduction, which mixture is passed through the glow discharge tube under the same processing conditions. The gaseous concentration of the dopants used was between about 5 x 10- 6 and 10-2 parts by volume It was found that the material thus deposited was extrinsic and of the N or p conduction type. Although these researchers did not know it, we know

  research by researchers other than hydro-

  The silane-containing gene combines at an optimal temperature with many unsaturated silicon bonds during glow discharge deposition, thereby substantially reducing the density of the localized states in the band gap to obtain amorphous material closest to the

  those of the corresponding crystalline material.

  The incorporation of hydrogen into the above process, however, has limits from the fixed ratio of hydrogen to silicon in the silane, and various configurations of the Si: H bond which introduce new anti-binding states. So there are limits

  fundamental to reducing the density of local conditions

in these materials.

  Highly improved amorphous silicon alloys having substantially reduced proportions have been prepared.

  located in their band intervals and presented

  both high-quality glow discharge electronic properties, as described in U.S. Patent No. 4,226,898 entitled Amorphous Semiconductors Equivalent to Crystalline Semiconductors (Stanford R Ovshinsky and Arun Madan-equivalent amorphous semiconductors), issued on the 7th

  October 1980, and by Deô: The viewfinder comíi e describes it com

  No. 4,217,374 issued under the same name to Stanford R Ovshinsky and Masatsugu Izu and issued August 12, 1980. As described in these patents, which are hereby incorporated by reference, fluorine is introduced into the art. amorphous silicon semiconductor alloy for substantially reducing the density of the localized states of this semiconductor The activated fluorine diffuses particularly easily and establishes bonds with the amorphous silicon in the amorphous body, which substantially reduces the density of the defective localized states contained because the small size, the high reactivity and the specificity of the chemical bonds of the fluorine atoms allows them to form an amorphous silicon alloy with even fewer defects. Fluorine bonds to unsaturated silicon bonds and forms what it is thought to be a stable, especially ionic bond with flexible bonding angles, which has as its result result in more stable and efficient compensation or modification than hydrogen and other

  Compensators Gtu modifiers Fluoride is also combined

  in a more preferred way with silicon and hydrogen, using hydrogen more desirably, because hydrogen has several options for its fluorine-free bonds, it is possible that hydrogen will It is desirable that the fluorine is a more effective compensating or modifying element than hydrogen. when used alone or with hydrogen because of its

  high reactivity, its specificity 4 in the chemical bond

  that, and its strong electronegativity.

  For example, compensation with fluorine alone or in combination with hydrogen is obtained by adding this or these elements in very small amounts (for example by fractions of one atomic percent). However, the amounts of fluorine and hydrogen that is used preferably are much larger than these little ones

  percentages so as to form an alloy of silicon-

  By way of example, the amounts of fluorine and hydrogen constituting the alloy may be between 1 and 5 percent or more. It is believed that the alloy thus formed comprises a lower density of defective states in band interval than that obtained by a simple neutralization of unsaturated bonds and defective states of the same type.

  particular that this significant amount of fluoride parti-

  important role in the new structural configuration.

  of a material containing amorphous silicon and facilitates the addition of other alloy materials such as

  Germanium In addition to its other

  Here, it is believed that fluorine is an organizer of the local structure of the silicon-containing alloy by means of inductive and ionic effects. It is believed that fluorine also influences hydrogen bonding by acting advantageously to reduce the density of the defective states, the hydrogen contributing to this action while acting as a reducing element of the density of the

  The ionic role played by fluorine in such an alliance

  ge is, it is believed, an important factor in

  view of the relationship with the nearest neighbor.

  Fluorine-containing amorphous silicon alloys have thus been shown to exhibit greatly improved characteristics for photovoltaic applications, compared with amorphous silicon alloys containing only hydrogen as a reducing element of states however, to get

  all the advantage of these amorphous silicon alloys

  3 When using fluoride when used to form the active regions of photovoltaic devices, it must be ensured that photon absorption takes place for the most part indoors for efficient generation of photovolts.

  pairs of electron-holes The above takes an important

  This type of device requires the deposition of p-type or n-type doped layers before and after the deposition of an intrinsic layer.

  doped layers on opposite sides of the inner layer

  active sque o are generated the pairs of electrons-

  holes establish a potential gradient across the device that facilitates the separation of electrons and holes and also form contact layers that facilitate the collection of electrons and holes under

form of an electric current.

  When the device is according to this structure, it is important that the p and N type layers are highly conductive and, at least in the case of the p-type layer, have a wide band gap, or band gap, to reduce the absorption of the photons of the p-type layer and thus obtain a stronger absorption in the active intrinsic layer. A p-type layer having a wide band gap is therefore extremely advantageous when the top layer of the device from which by passing solar energy, or when forming the lower layer of the device in conjunction with a rear reflective layer The rear reflective layers serve to reflect the unused light and return it to the

  intrinsic region of the device to enable the use

  more complete solar energy to generate additional electron-hole pairs A p-band wide-band layer allows a larger portion of the reflected light to penetrate the intrinsic active layer than the a p-type layer having no

not a wide band gap.

  Unfortunately, when the band interval of

  p-type amorphous silicon alloys increases, the conductivity

  In order to be effective in a

  photovoltaic power, an amorphous silicon alloy with

  band interval and type p must have a

  bandwidth 1.9 th V or higher Known amorphous silicon alloys, p-type and wide band gap,

  containing silicon, hydrogen, boron and car-

  high doping levels have conductivities of about 10-7 (A -cm) -1 When increasing the carbon concentration to widen the

  band, the resulting conductivity decreases.

  The Applicant has discovered broad band gap and p-type amorphous silicon alloys that are new and sophisticated, and have significantly higher conductivities than the broad band and p-type amorphous silicon alloy. known and mentioned above, for a band interval

  The alloys of this invention can be used.

  in single photovoltalic cell devices of p-i-n configuration, as well as in

  multiple cells comprising several individual cells

  Dual. The present invention creates broad band gap and p-type amorphous silicon alloys which are

  new and improved, with

  higher values and are intended for use in

  particularly in photosensitive devices

  In accordance with the present invention, the alloys comprise oxygen as an element which increases the band gap. The alloys of the present invention can be deposited by glow discharge decomposition.

  can incorporate other elements that increase the in-

  band, such as carbon, in

minor.

  The amorphous silicon alloys also incorporate at least one reducing element of the density of states such as

  than fluorine and / or hydrogen. The compensating

  modifiers or modifiers, and other elements, may be

added during the deposit.

  The wide band gap and p-type amorphous silicon alloys of the present invention further comprise a p-type dopant such as boron. Boron may be incorporated into the alloy starting from diborane (B 2 H 6).

  during glow discharge deposition.

  The alloys may incorporate a band-increasing element which is comprised of oxygen at concentrations ranging from one to thirty percent, resulting in bandwidths ranging from 1.7eV to For a given band interval, the alloys of the present invention have substantially higher conductivities than prior art broadband and p-type amorphous silicon alloys incorporating only carbon. in

  as an element that increases the band interval.

  Amorphous silicon alloys with a wide range of

  and p-type of the present invention are particularly

  They are useful in light-sensitive devices such as photovoltaic devices comprising an active region where photoelectrically generated pairs of electron-holes are formed. Because the alloys have large band gaps, only relatively small amounts of photons are absorbed therein. This allows for the absorption of a larger number of photons by the active region. As a result, the advantages of amorphous silicon-fluoride alloys for the active regions can be obtained. Because the alloys of the present invention have This results in a more efficient current collection of electrons and photoelectrically generated holes. Additionally, photovoltaic devices incorporating the improved alloy of the present invention may include a rear reflector for reflecting light. used

  in the intrinsic layer and create pairs of electrons-

  additional holes and generated photoelectrically.

  The short-circuit current of the devices incorporating

  The improved alloy of the present invention can be made even more important by adjusting the band gap of the active amorphous silicon alloys. The band gap adjusters can be added to the active or intrinsic alloys, so to adjust their band intervals, or to scale the band interval of the entire intrinsic body For example, one can add elements that decrease the band interval such as germanium, tin or lead the

  intrinsic alloy body, during deposition.

  You can also use the devices and the

  method of the present invention for making arrangements

  multi-celled cells, such as tandem cells.

  The band intervals of the inner layers can be adjusted

  in such a way that the current generation capacity of each cell can be maximized for a

  given and different part of the spectrum of

  lar. Accordingly, a first object of the invention is to provide a method for making an improved amorphous silicon alloy with a wide band and p-type gap. The method comprises depositing on a substrate a material comprising at least silicon, incorporating therein at least one state density reducing element and a p-type dopant, and introducing it into the material. the material of an element that increases the band interval,

  and it is characterized by the fact that the element which increases

  the band interval is oxygen, so

  produce a p-type amorphous silicon alloy

  oxygen in proportions between

and thirty percent.

  A second object of the invention is to create an improved amorphous silicon alloy with a wide band gap and p-type. The alloy comprises silicon, at least one reducing element of the density of states, a

  p-type dopant and at least one element that increases the

  The improvement is characterized by the fact that the element which increases the band gap is oxygen which is included in the alloy according to a

  percentage between one and thirty percent.

  A third object of the invention is to create, in a photosensitive device of the type comprising superposed layers of various materials and comprising a body

  amorphous semiconductor alloy forming a photo-layer

  sensitive and intrinsic sensitive on which can strike the radiation to produce charge carriers,

  and a layer of amorphous silicon alloy with a wide

  band and p-type vallevel adjacent to the intrinsic layer andcomprising at least one state density reducing element, a p-type dopant, and at least one element which increases the band interval The enhancement is

  characterized by the fact that the element which increases the inter-

  bandwidth is oxygen and the amorphous broad-band, p-type amorphous silicon alloy comprises oxygen in the range of from

and thirty percent.

  A fourth object of the invention is to create a multi-cell photovoltaic device formed from multiple layers of amorphous semiconductor alloys arranged on a substrate. The device comprises a plurality of individual cells arranged in series, each

  individual cell comprising a first layer of alloy

  doped amorphous semiconductor, a body of an intrinsic amorphous semiconductor alloy deposited on the first doped layer, another layer of semiconductor alloy

  doped amorphous material deposited on the intrinsic body and

  opposite to that of the first doped amorphous semiconductor alloy layer, and wherein at least one of the amorphous semiconductor alloy layers doped with at least one of the individual cells comprises an amorphous silicon alloy having a broad band and of type p having at least one state density reducing element, a p-type dopant, and at least one element which

  increases the band interval The device is characterized

  the fact that the element which increases the band gap is oxygen and that the amorphous wide-band and p-type amorphous silicon alloy comprises oxygen in a percentage between a

and thirty percent.

  FIG. 1 is a schematic representation of a glow discharge deposition system that can be used for carrying out the method of the present invention in order to produce the photovoltaic devices.

of the invention.

  Fig 2 is a section of a part of the system of the

  fig 1, according to the line 2-2 thereof.

  Fig. 3 is a graph showing the conductivity versus band gap curves for a broad band gap and known p-type amorphous silicon alloy as well as for a broad band gap amorphous silicon alloy and of type p realized

according to the present invention.

  Fig 4 is a section of a photovoltaic device

  p-i-n embodying the present invention.

  Fig 5 is a sectional view of another photovoltaic device

  talque p-i-n whose structure corresponds to that of a

  another embodiment of the invention.

  Fig. 6 is a sectional view of a multiple solar cell comprising a plurality of individual photovoltalic cells p-i-n arranged in a tandem configuration, and

according to the present invention.

  If we now refer more specifically to the

  fig 1, this represents a deposition system by

  A housing 12 surrounds a vacuum chamber 14 and has an inlet chamber 16 and an outlet chamber 18. A cathode support member 20 is mounted in the vacuum chamber 14.

with interposition of insulation 22.

  The support member 20 comprises an insulating sleeve 24 circumferentially surrounding the support member 20 A shield 26 defining a dark space is spaced from the sleeve 24 which circumferentially surrounds a substrate 28 is fixed to the inner end 30 of the support member, by means of a retaining element 32 The retaining element 32 can be screwed or fixed in any other known manner to the support member 20 and electrically contacted

with this one.

  The cathode support member 20 comprises a well 34 in which is inserted an electric heating element 36 for heating the support member 20 and thereby the substrate 28. The cathode support member 20 comprises

  Also, a temperature sensing probe 38 is

  The temperature probe 38 is used to control the temperature of the support member 20.

  the excitation of the heating element 36 and maintain the

  20 and the substrate 28 at the desired temperature. The system 10 also comprises an electrode 40 projecting from the housing 12 and entering the chamber

  vacuum 14 being spaced apart from the catheter support member

  The electrode 40 carries a shield 42 which surrounds it and which in turn supports a substrate 44. The electrode 40 comprises a well 46 in which is inserted an electrode heating element 48.

  a probe 50 sensitive to temperature and intended for measuring

  the temperature of the electrode 40 and therefore the

  The probe 50 is used to control the energy

  provided to Heating Element 48 and maintain the

  trode 40 and the substrate 44 at any desired temperature,

independently of the organ 20.

  A glow discharge plasma develops in a

  space 52 between the substrates 28 and 44 because of the

  generated by a regulated source of high frequency current, alternating current or direct current, which is coupled to the cathode support member 20 and thence, through the gap 52, to the electrode 40 which is connected to the

  The vacuum chamber 14 is evacuated to

  The manometer 58 is coupled to the vacuum system and used to control the pump 54 and maintain the system 10 at the desired pressure by a vacuum pump 54 coupled to the chamber 14 via a particle trap 56.

desired pressure.

  The inlet chamber 16 of the housing 12 is preferably provided with several pipes 60 intended to introduce

  substances in the system I 0 o they must be mixed

  The inlet chamber 16 may be located in the chamber 14, in the space 52 for the plasma of the glow discharge, on the substrates 28 and 44. If desired, the inlet chamber 16 may be located in a remote location and the gases may The gaseous substances are sent into the lines 60 via a filter or other purifying device 62 at a flow rate controlled by a flow rate.

valve 64.

  When a material is not initially in gaseous form, but in liquid or solid form, it may be placed in a sealed container 66, as indicated at 68. The material 68 is then heated by a heating element 70 to increase the vapor pressure in the container 66 A suitable gas such as

  argon is sent by a dip tube 72 into the material

  68 to capture the vapors of the material 68 and convey the vapors through a filter 62 'and a valve 64' to get into the pipes 60 and thence in the

system 10.

  The inlet chamber 16 and the outlet chamber 18 preferably comprise means 74 forming a screen and

  intended to retain the plasma in chamber 14 and principally

  between the substrates 28 and 44.

  The materials that are sent through the pipes 60 are mixed in the inlet chamber 16 and then sent into the space 52 is the glow discharge to maintain the plasma and deposit the alloy on the substrates, with incorporation of silicon, fluorine, oxygen and

  other desired modifying elements such as hydro-

  gene and / or dopants or other desired materials.

  In operation and to deposit layers of alloys

  In the case of intrinsic amorphous silicon, the system 10 is first pumped until it reaches a desired deposition pressure, for example less than 20 rpm before deposition. Starting materials or reaction gases Such as silicon tetrafluoride (Si F 4) and molecular hydrogen (H 2) and / or silane are fed into the inlet chamber 16 through separate pipes 60 and are then mixed into the chamber. The gas mixture is passed to the vacuum chamber to maintain a partial pressure of about 0.6 torr therein. A plasma is generated in the gap 52 between the substrates 28 and 44, using either a DC voltage greater than 1000 volts, ie a high frequency current of about 50 watts, this frequency being 13.56 MHz or any other desired value. In addition to the intrinsic amorphous silicon alloys deposited in the manner described above, the devices of the present invention illustrated in the various modes of

  which will be described later also use

  doped amorphous silicon alloys comprising the wide band gap amorphous silicon alloy

  and p-type of the present invention.

  doped geometry have a conductivity of the p, p +, N or n + type, and

  they can be formed by introducing an appropriate dopant

  in the vacuum chamber, with the intrinsic starting material such as silane (Si H 4) or tetrafluoride

  silicon (Si F 4), and / or hydrogen and / or silane.

  With regard to the N or p doped layers, the material

  The material can be doped with 5 to 100 ppm of doping material as it is deposited. To obtain n + or p + doped layers, the material is doped with a dopant material whose proportion is between 100 ppm and more than 1%. N-type dopants can be phosphorus, arsenic, antimony or bismuth.

  N-doped layers are preferably deposited by decomposition

  by glow discharge of silicon tetrafluoride

  cium (Si F 4) and phosphine (PH 3) at least One can also

  addition to this mixture of hydrogen and / or

silane (Si H 4).

  The p-type dopants may be boron, aluminum or

  gallium, indium or thallium.

  this, the p-type doped layers are deposited by decomposition

  by glow discharge of silane and diborane (B 2 H 6) at least, or silicon tetrafluoride and diborane can also be added to the tetrafluoride of

  silicon and diborane hydrogen and / or silane.

  In addition to the above and according to the present invention,

  p-type doped layers are formed from amorphous silicon alloys containing oxygen as an element which increases the band interval of this

  In fact, we add to each of the gaseous mixtures indicated below

  above oxygen diluted with argon For example, an amorphous silicon alloy with wide band gap and p-type can be formed by means of a gaseous mixture containing 94.6% silane (Si H 4) , 5.2% diborane (B 2 H 6) and 0.2% oxygen. Thus, a p-type amorphous silicon alloy having a band gap greater than 1.9 e V is obtained. % oxygen by diluting the oxygen

  in argon This level of oxygen in the gas phase

  l U is translated into an amorphous silicon alloy incorporating

  in the film about 10% oxygen.

Various mixtures of gases having from 0.01% to 1% of the gaseous mixture can be used with oxygen. This range results correspondingly in concentrations ranging from

  from 1% to 30% oxygen in the deposited films.

  The increase in conductivity of the new and improved alloys of the present invention is particularly apparent in FIG. 3. the curve of the

  conductivity with respect to the band gap is indi-

  for new alloys that contain oxygen as an element that increases the band gap, and for the known broad-band, p-type, amorphous silicon alloy that contains only carbon as element that increases the band interval It will be noted that

  for a given band interval, the new alloy pre-

  It has also been observed that amorphous silicon alloys with a wide band-gap and a p-type range containing both oxygen and carbon have higher conductivities than those of the known alloy. which only incorporate carbon as an element that increases the band gap However, in these films, only

  minor amounts of carbon have been incorporated into

  In the above, it can be seen that oxygen serves not only as an element which increases the band gap in p-type amorphous silicon alloys, but also as alloys. of broad band gap and p-type amorphous silicon which include oxygen as an element

  which increase the band gap have a conductivity

  superior to that of amorphous silicon alloys with wide band and p-type

  of oxygen and belonging to the prior art.

  The doped layers of the devices are deposited at

  various temperatures between 2000 C and 10000 C envi-

  L O ron, depending on the shape of the material used and the type

  of the substrate used When it comes to aluminum substrates

  the temperatures used should not exceed about 6000 ° C., and when it is stainless steel, they can exceed about 10000 ° C. As regards the intrinsic and doped alloys, initially compensated by hydrogen, such as those which are deposited from a

  starting material consisting of silane gas, the temperature

  the substrate must be less than about 4000 C and

  preferably between 2500 ° C. and 350 ° C.

  Other materials and alloying elements may also

  These other materials and elements are described below in connection with the various configurations of the devices

  the present invention and illustrated in FIGS. 4 to 6.

  Referring now to FIG.

  cross section a device p-i-n structured according to a pre-

  first embodiment of the present invention.

  110 comprises a substrate 112 which may be made of glass or a flexible web made of stainless steel or aluminum. The substrate 112 has the width and the length

  desired, and its thickness is preferably 0.075 mm.

  The electrode 114 is deposited on the substrate 112 to

  to form a rear reflector for the cell 110

  The rear reflector layer 114 is deposited by vapor deposition which is a relatively fast deposition method. Preferably, the rear reflector layer is constituted by a reflective metal such as silver, aluminum or aluminum.

  It is best to use the reflective layer

  because in a solar cell, the light that is not absorbed and which passes through the device is reflected by the rear reflector 114 and passes again in the device which then absorbs more light energy and

  increases the efficiency of the device.

  Substrate 112 is then placed in the glow discharge deposition environment. A first p-band wideband amorphous silicon 116 layer is deposited on the rear reflective layer 114 of the present invention. It is represented that it is of p + conductivity. The p + region is as thin as possible, its thickness being of the order of 50 to 150 angstroms, which is sufficient for the

  p + region establishes a good ohmic contact with the reflec-

  The p + region 116 also serves to establish a potential gradient across the device to facilitate the collection of photoelectrically induced electron-hole pairs in the form of an electric current. The p + region 116 can be deposited from the any of the gas mixtures which have been previously indicated with a view to

  depositing this material according to the present invention.

  A body is then deposited in an intrinsic amorphous silicon alloy 118 on the p-type layer 116

  band interval The intrinsic body 118 is related to

  is thick and of the order of 4500 Å, and is deposited from silicon tetrafluoride and hydrogen and / or

  silane Preferably, the intrinsic body contains the

  fluorine-compensated amorphous silicon bonding where the majority of electron-hole pairs are generated The short circuit current of the device is enhanced by the effects

  rear reflector 114 and the strong conductor

  tivity of the improved amorphous silicon alloy

  band and p-type range of the present invention.

  Another doped layer 120 whose conductivity is opposite to that of the first doped layer 116 is deposited on the intrinsic body 118 It comprises an amorphous silicon alloy of n + conductivity The n + layer 120 is deposited from any of the mixtures The n + 120 layer is deposited until its thickness is between 50 and 500 Angstr 5 ms, and it serves as a contact layer.

  The layer n + 120 is then deposited with a layer of oxy-

  The OCT layer 122 may be deposited in a vapor deposition environment and may consist for example of indium tin oxide (OIE), cadmium stannate ( Cd 25 n O 4),

  or doped tin oxide (Sn O 2).

  A gate electrode 124 made of a metal of good electrical conductivity is deposited on the surface of the OCT layer 122.

  orthogonally connected lines of conductive material

  only a minor part of the surface of the metal region, the rest of which must be exposed to solar energy. For example, the grid 124 can occupy only

  from 5 to 10% of the total area of the metal-

  The gate electrode 124 collects in a unique manner

  form the current from the OCT layer 122 so as to give the device a good low-level series resistance. To end the device 110, an anti-reflection (AR) layer 126 is applied to the gate electrode 124 and to the

  OCT 122 surfaces lying between the

  The AR layer 126 comprises a surface of incidence of solar radiation on which solar radiation is struck. For example, the

  AR layer 126 may have a thickness of the order of magnitude

  of the wavelength of the maximum energy point of the solar radiation spectrum divided by four times the refractive index of the antireflection layer 126 A suitable AR layer 126 may be constituted by zirconium oxide. having a thickness of about 500 A and a

refractive index of 2.1.

  It is possible to adjust the band interval of the intrinsic layer 118 to obtain specific photosensitive characteristics. For example, one or more elements which reduce the band gap, such as germanium, may be incorporated in the intrinsic layer. , tin or lead, to reduce its band gap (see for example US Patent No. 4,342,044 issued to Stanford R Ovshinsky and Masatsugu Izu on July 27, 1982 and entitled "Method for Optimizing Photoresponsive"). Amorphous Alloys and Devices "'Process to optimize alloys and amorphous devices

  1 l photosensitive ") This result can be obtained by introducing

  for example germane gas (Ge H 4) in the mixture

  gas from which the layer 118 is deposited.

  Referring now to FIG.

  Another apparatus 130 embodies the present invention. The device 130 is similar to the device of FIG. 3, except that it does not include a rear reflector and the p + and n + layers are inverted.

  of the device 130 may be stainless steel, for example

  If desired, a reflective layer may be deposited on the substrate 132 by any of the methods previously referred to with respect to such a layer, and may be formed

  from silver, aluminum or copper for example.

  A first doped layer 134 whose conductivity is n +, as illustrated, is deposited on the substrate 132. If desired, the n + layer 134 may incorporate an element that increases the band gap, such as nitrogen or phosphorus.

  carbon, so as to form a n + layer with a large

the band.

  An intrinsic body 136 is deposited on the n + layer 134 and as for the intrinsic body 118 of the device 110, it preferably comprises an amorphous silicon-fluorine alloy

of similar thickness.

  Another doped layer 138 whose conductivity is opposite to that of the first doped layer 134 and which is preferably a wide band gap p + layer incorporating oxygen according to the present invention is

  deposited on the intrinsic body 136.

  The device is terminated by forming an OCT layer 140 on the p + layer 138, and a gate electrode 142. These operations can be performed in the manner described with

  reference to the device 110 of FIG.

  As in the case of the previous embodiment, the band interval of the intrinsic layer 136 can be adjusted to obtain a particular photosensitive feature, incorporating decreasing elements.

  As a further alternative, the band interval

  Intrinsic body bandwidth 136 may be graduated so as to gradually increase from layer n + 134 to the other layer n + 138 (see, for example, associated U.S. Patent Application No. 4,272,756 to Stanford R Ovshinsky and David Adler on September 29, 1982, entitled "Methods for Grading the Band Gaps of Amorphous Alloys and Devices"

  strip intervals of alloys and amorphous devices ").

  For example, when the intrinsic layer 136 is deposited,

  it can be incorporated in alloys and according to a concentration

  gradually decreasing one or more elements which decrease the band gap, such as germanium, tin or lead. For example, germane gas (Ge H 4) can be introduced into the glow discharge deposition chamber. starting from a relatively high concentration at the beginning and gradually decreasing as the intrinsic layer is deposited, to a point where this introduction is terminated. The resulting intrinsic body therefore contains an element which reduces the band interval, such as germanium, in concentrations that gradually decrease from

  the n + layer 134 and towards the p + layer 138.

  Referring now to FIG.

  a multiple-cell device 150 shown in section and configured in tandem.

  comprises two individual cells 152 and 154

  in series and implementing the present invention.

  As can be seen, multiple units can be used

  comprising more than two individual cells.

  The device 150 comprises a substrate 156 formed from a metal with good electrical conductivity such as stainless steel or aluminum for example. On the substrate 156 is deposited a rear reflector 157 which can be formed as The first unit cell 152 comprises a first p + type doped amorphous silicon alloy layer 158 deposited on the rear reflector 157. The p + layer is preferably an amorphous silicon alloy with a wide band gap.

  p-type according to the present invention may be deposited

  from any of the starting materials

  previously mentioned for depositing this material.

  A first body made of an intrinsic silicon alloy

  amorphous 160 is deposited on the p + layer 158 with broad inter-

  bandvalue The first body of intrinsic alloy 160

  is preferably a silicon alloy

amorphous fluorine.

  Another layer of doped amorphous silicon alloy 162 is deposited on the intrinsic layer 160 Its conductivity is opposite to the conductivity of the first doped layer

  158 and therefore constitutes an n + layer.

  The second unit cell 154 is essentially identical and comprises a first p + doped layer 164, an intrinsic body 166 and another n + doped layer 168. The device 150 is terminated by an OCT layer 170, a

  gate electrode 172 and an anti-reflection layer 174.

  The band intervals of the intrinsic layers are preferably adjusted so that the band interval of the layer 166 is larger than the band interval.

  layer 160 For this purpose, the formation layer of

  linkage 166 may comprise one or more elements that increase the band gap, such as nitrogen and

  carbon The intrinsic alloy that forms the intrinsic layer

  160 may include one or more elements which

  the band interval, such as germanium, of

tain or lead.

  It can be deduced from the figure that the intrinsic layer of the cell is thicker than the intrinsic layer 166. This makes it possible to use, for the generation of electron-hole pairs, the entire usable spectrum.

solar energy.

  Although a tandem cell embodiment has been shown and described here, unit cells can also be isolated from each other by layers.

  oxide, for example, so as to form a multi-cell

  stacked each cell could include a pair of collector electrodes to facilitate serial linkage

  cells with external wiring.

  As another variant and as mentioned with reference to the individual cells previously described, one or more of the intrinsic bodies of the unit cells may comprise alloys whose band intervals are caused to gradually vary.

  can incorporate into the intrinsic alloys some

  One or more of the above-mentioned elements that increase or decrease the band gap. Reference can also be made to U.S. Patent Application No. 427,757, filed on behalf of Stanford R Ovshinsky and David Adler on September 29, 1982, entitled Multiple Cell. Photoresponsive Amorphous Alloys and Devices "(Alloys and

  multi-cell photosensitive amorphous devices).

  For each embodiment of the invention that is described herein, the alloy layers other than the intrinsic alloy layers may not be layers.

  amorphous and be for example polycrystalline layers.

  (The term "amorphous" here refers to an alloy or material having a large amplitude disorder, although it may include a short or intermediate order-or even

  sometimes contain some crystalline inclusions).

  Modifications and variations can be made to the present invention, in the context of the teaching described above It will therefore be understood that the invention can be implemented differently than those which have been specifically described provided that they remain in the

scope of the appended claims.

Claims (24)

CLAIMS.   A process for manufacturing an improved amorphous silicon alloy with a wide band gap and p-type, said method comprising depositing on a substrate a material comprising at least silicon, incorporating into said material at least one element reducer of the   density of states and a p-type dopant, and the introduc-   in said material of an element which increases the inter-   bandwidth, said method being characterized in that   the element that increases the band gap is oxy-   gene, so as to produce a p-type amorphous silicon alloy comprising oxygen in proportions   between one and thirty percent.   2 Process according to Claim 1, characterized in that the element or elements reducing the density of the states   is or consist of hydrogen.   3 Process according to Claim 1, characterized in that the element or elements reducing the density of the states   is od are constituted by fluorine.   4 Process according to claim 3, characterized by the introduction of a second density reducing element   states, this second element being hydrogen.   Process according to one of Claims 1 to 4,   characterized in that the p-type dopant is boron.   Process according to one of claims 1 to 5,   in that the alloy is deposited by glow discharge   from at least one mixture of Si H 4, B 2 H 6 and oxygen. Process according to Claim 6, characterized in that the oxygen concentration in the mixture is included between 0.01 and 1%.   The process according to one of claims 1 to 5, which is   in that the alloy is deposited by light discharge   nescente from at least one mixture of Si F 4, Si H 4, B> H 6 and oxygen.   9 Process according to claim 8, characterized in that the concentration of oxygen in the mixture is included between 0.01 and 1 percent.   Process according to one of S reve N di cations 1 to 9, characterized by the incorporation of a second element which increases the band gap, in minor amounts compared with the amount of oxygen incorporated, said second element which increases the band gap being carbon. An improved amorphous silicon, wide band-gap and p-type silicon comprising at least one state density reducing element, a p-type dopant, and at least one element which increases the band gap characterized in that the element which increases the band gap is oxygen, and in that the alloy comprises said oxygen   in proportions between one and thirty percent.   12 Alloy according to claim 11, characterized in that the reducing element (s) of the density of the states   is or consist of hydrogen.   13 Alloy according to claim 11, characterized in that the reducing element (s) of the density of the states   is or consist of fluorine.   14 Alloy according to claim 13, characterized in that it is incorporated therein a second reducing element of the   density of states, this element being hydrogen.   Alloy according to one of Claims 11 to 14,   characterized in that the p-type dopant is constituted by boron.   An alloy according to one of claims 11 to 15,   Characterized by a second element which increases the band gap, in a minor concentration as compared to   the concentration of oxygen, this second element which increases   the band gap is made of carbon.   In a photosensitive device of the type comprising superposed layers of various materials deposited on a   substrate comprising a amorphous semiconductor alloy body   phe which forms an active and intrinsic photosensitive layer on which the radiation can be struck to produce charge carriers, and a layer of broad band gap and p-type amorphous silicon alloy (116, 138) adjacent to said intrinsic layer (118, 136) comprising at least one state density reducing element, a p-type dopant, and at least one element which increases the band gap, said improvement characterized in that said element which increases the band gap is constituted by oxygen and in that said broad-band and p-type amorphous silicon alloy comprises hydrogen in proportions between one and thirty percent.   Apparatus according to claim 17, characterized by an N-type amorphous silicon alloy layer (120, 134) adjacent to said intrinsic layer on its side which is opposed to said amorphous silicon alloy layer to   wide range of band and p-type (116, 138).   Apparatus according to claim 18, characterized by a rear reflective layer (114) adjacent to said p-type or n-type amorphous silicon alloy layer,   on its side which is opposite to said intrinsic layer.   Device according to one of claims 17 to 19,   characterized in that the reducing element of the density of   states is made up of hydrogen.   Device according to one of claims 17 to 19,   characterized in that the reducing element of the density of states is constituted by fluorine.   Apparatus according to claim 21, characterized in that the amorphous wide band gap and p-type amorphous silicon layer (116, 138) further comprises a second state density reducing element, said second reducing element of the density of states being consisting of hydrogen.   Apparatus according to one of claims 17 to 22,   characterized in that the p-type dopant is constituted by boron.   24 Device according to one of claims 17 to 23,   characterized in that the broad band gap and p-type amorphous silicon alloy layer (116, 138)   additionally includes a second element which increases   bandvalue, in minor concentrations compared to the concentration of oxygen, this second element which increases the band gap being constituted by carbon. Multi-cell photovoltalic device formed from multiple layers of semiconductor alloys   amorphous material deposited on a substrate, said device comprising   a plurality of individual cells (152, 154) arranged in series, each of said individual cells comprising a first amorphous and doped semiconductor alloy layer (158, 164), a body of an amorphous semiconductor alloy   intrinsic (160, 166) deposited on the first doped layer,   and another layer of doped amorphous semiconductor alloy   (162, 168) deposited on the intrinsic body and   opposite to that of the first doped amorphous semiconductor alloy layer, and in that at least one of said doped amorphous semiconductor alloy layers and at least one of said individual cells comprises an amorphous silicon alloy with a broad band and p-type interval comprising at least one reducing element of the   density of states, a p-type dopant and at least one   which increases the band interval, said device   being characterized in that the element that increases the inter-   bandwidth e-st constituted by oxygen, and in that the amorphous silicon alloy with wide band gap and   of type p comprises oxygen in   taken between one and thirty percent.   Device according to claim 25, characterized in that the amorphous broad-band and p-type amorphous silicon alloy comprises a second element which increases the band gap, in minor concentrations compared to the concentration of the oxygen, this second element which increases the band gap being constituted by carbon.   Apparatus according to one of claims 25 or 26,   characterized in that the reducing element of the density of   states is made up of hydrogen.   Device according to one of claims 25 or 26,   characterized in that the reducing element of the density of states is constituted by fluorine.   29 Apparatus according to claim 28, characterized in that the amorphous silicon alloy with wide band interval and p type comprises a second reducing element of the density of states, this second reducing element of the   density of states being constituted by hydrogen.   Device according to one of Claims 25 to 29,   characterized by a rear reflective layer (157) which   is immediately adjacent to the substrate (156).   31 Apparatus according to one of claims 25 to 30,   characterized in that each intrinsic body (160, 166) comprises a band gap and in that at least one of said intrinsic bodies comprises a band gap   set to a photosensitive wavelength characteristic specific.